Authors: David Eagleman
By the same token, to know oneself may require a change of definition of “to know.” Knowing yourself now requires the understanding that the conscious
you
occupies only a small room in the mansion of the brain, and that it has little control over the reality constructed for you. The invocation to know thyself needs to be considered in new ways.
Let’s say you wanted to know more about the Greek idea of knowing thyself, and you asked me to explain it further. It probably wouldn’t be helpful if I said, “Everything you need to know is in the individual letters: γ ν ẃ θ ι σ ε α υ τ ό ν.” If you don’t read Greek, the elements are nothing but arbitrary shapes. And even if you
do
read Greek, there’s so much more to the idea than the letters—instead you would want to know the culture from which it sprung, the emphasis on introspection, the suggestion of a path to enlightenment.
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Understanding the phrase requires more than learning the letters. And this is the situation we’re in when we look at trillions of neurons and their sextillions of voyaging
proteins and biochemicals. What does it mean to know ourselves from that totally unfamiliar perspective? As we will see in a moment, we need the neurobiological data, but we also need quite a bit more to know ourselves.
Biology is a terrific approach, but it’s limited. Consider lowering a medical scope down your lover’s throat while he or she reads poetry to you. Get a good, close-up view of your lover’s vocal chords, slimy and shiny, contracting in and out in spasms. You could study this until you were nauseated (maybe sooner rather than later, depending on your tolerance for biology), but it would get you no closer to understanding why you love nighttime pillow talk. By itself, in its raw form, the biology gives only partial insight. It’s the best we can do right now, but it’s far from complete. Let’s turn to this in more detail now.
One of the most famous examples of brain
damage comes from a twenty-five-year-old work-gang foreman named
Phineas Gage. The
Boston Post
reported on him in a short article on September 21, 1848, under the headline “Horrible Accident”:
As Phineas P. Gage, a foreman on the railroad in Cavendish, was yesterday engaged in tamping for a blast, the powder exploded, carrying an instrument through his head an inch and a fourth in [diameter], and three feet and [seven] inches in length, which he was using at the time. The iron entered on the side of his face, shattering the upper jaw, and passing back of the left eye, and out at the top of the head.
The iron tamping rod clattered to the ground twenty-five yards away. While Gage wasn’t the first to have his skull punctured and a portion of his brain spirited away by a projectile, he was
the first to not die from it. In fact, Gage did not even lose consciousness.
The first physician to arrive, Dr.
Edward H. Williams, did not believe Gage’s statement of what had just happened, but instead “thought he [Gage] was deceived.” But Williams soon understood the gravity of what had happened when “Mr. G. got up and vomited; the effort of vomiting pressed out about half a teacupful of the brain, which fell upon the floor.”
The Harvard surgeon who studied his case, Dr. Henry Jacob Bigelow, noted that “the leading feature of this case is its improbability.… [It is] unparalleled in the annals of surgery.”
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The
Boston Post
article summarized this improbability with just one more sentence: “The most singular circumstance connected with this melancholy affair is that he was alive at 2:00 this afternoon, and in full possession of his reason, and free from pain.”
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Gage’s survival alone would have made an interesting medical case; it became a famous case because of something else that came to light. Two months after the accident his physician reported that Gage was “feeling better in every respect … walking about the house again; says he feels no pain in the head.” But foreshadowing a larger problem, the doctor also noted that Gage “appears to be in a way of recovering, if he can be controlled.”
What did he mean, “if he can be controlled”? It turned out that the preaccident Gage had been described as “a great favorite” among his team, and his employers had hailed him as “the most efficient and capable foreman in their employ.” But after the brain change, his employers “considered the change in his mind so marked that they could not give him his place again.” As Dr.
John Martyn Harlow, the physician in charge of Gage, wrote in 1868:
The equilibrium or balance, so to speak, between his intellectual faculties and animal propensities, seems to have been destroyed. He is fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint or advice when
it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating, devising many plans of future operations, which are no sooner arranged than they are abandoned in turn for others appearing more feasible. A child in his intellectual capacity and manifestations, he has the animal passions of a strong man. Previous to his injury, although untrained in the schools, he possessed a well-balanced mind, and was looked upon by those who knew him as a shrewd, smart businessman, very energetic and persistent in executing all his plans of operation. In this regard his mind was radically changed, so decidedly that his friends and acquaintances said he was “no longer Gage.”
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In the intervening 143 years we have witnessed many more of nature’s tragic experiments—strokes, tumors, degeneration, and every variety of brain injury—and these have produced many more cases like Phineas Gage’s. The lesson from all these cases is the same: the condition of your brain is central to who you are. The
you
that all your friends know and love cannot exist unless the transistors and screws of your brain are in place. If you don’t believe this, step into any neurology ward in any hospital. Damage to even small parts of the brain can lead to the loss of shockingly specific abilities: the ability to name animals, or to hear music, or to manage risky behavior, or to distinguish colors, or to arbitrate simple decisions. We’ve already seen examples of this with the patient who lost the ability to see motion (
Chapter 2
), and the Parkinson’s gamblers and frontotemporal shoplifters who lost the ability to manage risk-taking (
Chapter 6
). Their essence was changed by the changes in their brain.
All of this leads to a key question: do we possess a
soul that is separate from our physical biology—or are we simply an enormously complex biological network that mechanically produces our hopes, aspirations, dreams, desires, humor, and passions?
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The majority of people on the planet vote for the extrabiological soul, while the majority of neuroscientists vote for the latter: an essence
that is a natural property that emerges from a vast physical system, and nothing more besides. Do we know which answer is correct? Not with certainty, but cases like Gage’s certainly seem to weigh in on the problem.
The
materialist
viewpoint states that we are, fundamentally, made only of physical materials. In this view, the brain is a system whose operation is governed by the laws of chemistry and physics—with the end result that all of your thoughts, emotions, and decisions are produced by natural reactions following local laws to lowest potential energy. We are our brain and its chemicals, and any dialing of the knobs of your neural system changes
who you are
. A common version of materialism is called
reductionism
; this theory puts forth the hope that we can understand complex phenomena like happiness, avarice, narcissism, compassion, malice, caution, and awe by successively
reducing
the problems down to their small-scale biological pieces and parts.
At first blush, the reductionist viewpoint sounds absurd to many people. I know this because I ask strangers their opinion about it when I sit next to them on airplanes. And they usually say something like “Look, all that stuff—how I came to love my wife, why I chose my job, and all the rest—that has nothing to do with the chemistry of my
brain
. It’s just
who I am
.” And they’re right to think that the connection between your essence as a person and a squishy confederacy of cells seems distant at best. The passengers’ decisions came from
them
, not a bunch of chemicals cascading through invisibly small cycles. Right?
But what happens when we crash into enough cases like Phineas Gage’s? Or when we turn the spotlight on other influences on the brain—far more subtle than a tamping rod—that change people’s personalities?
Consider the powerful effects of the small molecules we call narcotics. These molecules alter consciousness, affect cognition, and navigate behavior. We are slave to these molecules. Tobacco, alcohol, and cocaine are self-administered universally for the purpose of mood changing. If we knew nothing else about neurobiology, the
mere existence of narcotics would give us all the evidence we require that our behavior and psychology can be commandeered at the molecular level. Take
cocaine as an example. This drug interacts with a specific network in the brain, one that registers rewarding events—anything from slaking your thirst with a cool iced tea, to winning a smile from the right person, to cracking a tough problem, to hearing “Good job!” By tying positive outcomes to the behaviors that led to them, this widespread neural circuit (known as the mesolimbic
dopamine system) learns how to optimize behavior in the world. It aids us in getting food, drink, and mates, and it helps us navigate life’s daily decisions.
*
Out of context, cocaine is a totally uninteresting molecule: seventeen carbon atoms, twenty-one hydrogens, one nitrogen, and four oxygens. What makes cocaine
cocaine
is the fact that its accidental shape happens to fit lock-and-key into the microscopic machinery of the reward circuits. The same goes for all four major classes of drugs of abuse:
alcohol, nicotine, psychostimulants (such as amphetamines), and opiates (such as morphine): by one inroad or another, they all plug into this reward circuitry.
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Substances that can give a shot in the arm to the mesolimbic dopamine system have self-reinforcing effects, and users will rob stores and mug elderly people to continue obtaining these specific molecular shapes. These chemicals, working their magic at scales one thousand times smaller than the width of a human hair, make the users feel invincible and euphoric. By plugging into the dopamine system, cocaine and its cousins commandeer the reward system, telling the brain that this is the best possible thing that could be happening. The ancient circuits are hijacked.
The cocaine molecules are hundreds of millions of times smaller than the tamping rod that shot through Phineas Gage’s brain, and yet the lesson is the same: who you are depends on the sum total of your neurobiology.
And the
dopamine system is only one of hundreds of examples. The exact levels of dozens of other neurotransmitters—for example,
serotonin—are critical for who you believe yourself to be. If you suffer from clinical depression, you will probably be prescribed a medication known as a selective serotonin reuptake inhibitor (abbreviated as an SSRI)—something such as
fluoxetine or
sertraline or
paroxetine or
citalopram. Everything you need to know about how these drugs work is contained in the words “uptake inhibitor”: normally, channels called transporters take up serotonin from the space between neurons; the inhibition of these channels leads to a higher concentration of serotonin in the brain. And the increased concentration has direct consequences on cognition and emotion. People on these medications can go from crying on the edge of their bed to standing up, showering, getting their job back, and rescuing healthy relationships with the people in their life. All because of a subtle fine-tuning of a
neurotransmitter system.
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If this story weren’t so common, its bizarreness could be more easily appreciated.
It’s not just neurotransmitters that influence your cognition. The same goes for
hormones, the invisibly small molecules that surf the bloodstream and cause commotion at every port they visit. If you inject a female rat with estrogen, she will begin sexual seeking;
testosterone in a male rat causes aggression. In the previous chapter we learned about the wrestler
Chris Benoit, who took massive doses of testosterone and murdered his wife and his own child in a hormone rage. And in
Chapter 4
we saw that the hormone
vasopressin is linked to fidelity. As another example, just consider the hormone fluctuations that accompany normal menstrual cycles. Recently, a female friend of mine was at the bottom of her menstrual mood changes. She put on a wan smile and said, “You know, I’m just not myself for a few days each month.” Being a neuroscientist, she then reflected for a moment and added, “Or maybe
this
is the real me, and I’m actually someone else the other twenty-seven days of the month.” We laughed. She was not afraid to view herself as the sum total of her chemicals at any moment. She
understood that what we think of as
her
is something like a time-averaged version.
All this adds up to something of a strange notion of a self. Because of inaccessible fluctuations in our biological soup, some days we find ourselves more irritable, humorous, well spoken, calm, energized, or clear-thinking. Our internal life and external actions are steered by biological cocktails to which we have neither immediate access nor direct acquaintance.